1. Field of the Invention
The present invention relates to an apparatus for a stepwise periodic feeding of a strip-like workpiece, having a first pressing member adapted to periodically exert a pressure onto the workpiece, further having a second, periodically driven pressing member which co-operates with the first pressing member, which two pressing members are adapted to receive the strip-like workpiece between themselves for a periodic clamping and feeding of same, and having a periodically moveable first arresting member which is adapted to periodically press the strip-like workpiece against a second arresting member in order to temporarily arrest the strip-like workpiece.
2. Description of the Prior Art
Apparatuses for a stepwise periodic feeding of a strip-like workpiece are used together with presses in which presses a variety of tools for a working or processing, respectively of a strip-like workpiece can be mounted. Such a press is commonly called in the art punch press. The stepwise feeding of the strip-like workpiece to be worked upon or processed, respectively in the punch press proceeds either by oscillating rollers or by tongs. For a feeding movement the strip-like workpiece is clamped between two rollers or by the tongs. In designs having rollers, the rollers rotate in an oscillating manner through a predetermined angle to and fro around their longitudinal axes. In designs having tongs an oscillating rectilinear movement to and fro of the tongs is performed. In order to perform the feeding movement of the strip-like workpiece or web, respectively, it is clamped between the rollers or tongs, respectively, and is advanced. After the advancing movement has been terminated the clamping is released and the rollers or tongs, respectively, return to their initial position. In order to keep the web arrested during this return movement it is clamped by arresting members, generally by a vertically moveable clamping bar which clamps the web against a counter member in order to keep it arrested. Furthermore, in order to prevent an adding up of small feeding errors such to prevent a detrimental influence regarding the precision of the article produced by the working of the web, so-called guiding pin holes are punched e.g. during each process step, such as a punching into the striplike web, whereby immediately prior to each process step, e.g. a punching operation, the strip-like workpiece is guided and located precisely by positioning pins which enter into the guiding pin holes such that the tools of the punch press can process the web with a sufficient precision. As long as the string-like web is arrested by the guiding pins, neither the feeding members nor the arresting members are allowed to act onto the strip-like web, all these members are lifted off the strip-like web during the processing or working, respectively phase, which state of operation is called intermediate lifting.
The driving of the oscillating feeding rollers or tongs, respectively, takes place such as generally known by means of a crank drive arrangement or an oscillating cam drive apparatus.
In the case of known feeding apparatuses having a crank drive, a sine-like motion of the feeding movement occurs during a movement of the crank angle through 180.degree., whereby at the end positions of the movement a "momentary standstill" and maximal acceleration occurs.
Other designs of feeding apparatuses comprise an oscillating cam drive in order to produce the feeding movement, i.e. the movements of the rollers or tongs, respectively. The advantage of an oscillating cam drive is that the angle of feed can be selected to be larger or less than 180.degree., because contrary to a crank drive the motion in the oscillating cam drive can be variously selected.
Accordingly, an arbitrarily long standstill of the feeding members of an acceleration of 0 can be set at the end position of the feeding movement. The flexibility of the selecting of the movement of the feeding members can doubtlessly be increased therewith, but the performance of the feed will be lessened accordingly, because a standstill of a more or less long duration during the end phases of the feeding movement takes place.
At known feeding apparatuses having an oscillating cam drive the periodic movements, at the one hand of the feeding members, i.e. rollers or tongs, and at the other hand the arresting members, thus the clamping bar with the counter member are each controlled by a separate cam drive. Because now the course of their movements differ from each other they must be precisely co-ordinated among themselves, whereby at the end positions of the feeding movement a standstill of the rollers or tongs, respectively, and an acceleration of 0 must be present. Such a standstill leads to a corresponding reduction of the performance of the feeding and accordingly to a corresponding reduction of the output of the production when processing a respective web-shaped workpiece.
A curve generated by the guiding members of an oscillating cam drive which corresponds to the curve generated by a crank drive (sine movement) with a "momentary standstill" and maximal acceleration in the end positions is not possible.